Optimal functioning of an internal combustion engine (e.g., a diesel engine) requires that combustion acids, e.g. carboxylic, nitric, nitrous, sulfuric and sulfurous acid, with or without alkyl groups, be neutralized where or near where they first contact the lubricant, i.e., near the piston. In the absence of this acid neutralization, the engine corrodes, the lubricant gels, the viscosity rapidly increases, and engine deposits form. These actions result in increased oil consumption and engine wear.
Traditionally, metal-containing detergents, such as barium, calcium, or magnesium overbased sulfonates or phenates, neutralize combustion acids in lubricant systems. (See U.S. Pat. Nos. 2,316,080; 2,617,049; 2,647,889; and 2,835,688). In lubricants where metal detergents are absent, polyethyleneamine based dispersants or other ashless dispersants neutralize combustion acids. (See U.S. Pat. No. 3,172,892). At the loadings needed to effectively neutralize combustion acids in internal combustion engine lubricants, ashless detergents are less cost effective than ash-containing detergents. As a consequence, ashless dispersants are relegated mainly to the purpose of maintaining engine cleanliness, where their cost is less of an issue.
Well formulated lubricants containing metal detergents are very effective in neutralizing combustion acids. This neutralization helps to prevent corrosion and reduce piston deposits. At high detergent concentrations, however, metal detergents begin to deposit on pistons offsetting desired detergency improvements. For example, the deposits on some pistons contain up to 34% calcium and magnesium derived from the detergent. See A. Schetelich et. al., “The Control of Piston Crown Land Deposits in Diesel Engines Through Oil Formulation,” Soc. Automat. Eng. Tech., Pub. Ser. 861517 (1986).
U.S. Pat. Nos. 4,906,389; 5,068,044; 5,069,799; and 5,164,101 disclose the use of a strong base located in the oil filter. Combustion acids passing by the piston are thought to be neutralized by a weak base additive in the dispersant. Dispersant contained in the oil carries the combustion acid to the strong base in the filter. In the oil filter, the combustion acid transfers from the weak base dispersant to the strong base and is sequestered. The dispersant remains in the lubricant and passes back to the piston where it may neutralize additional combustion acid. At the same time, ash-containing detergent in the oil is neutralizing combustion acid and transporting it to the filter where it may be sequestered. To the degree that combustion acid is sequestered in the oil filter, certain advantages may arise. First, additional combustion acid may be neutralized without increasing the concentration of the ash-containing detergent. Second, the interval between oil drains may be increased. Third, the concentration of the ash-containing detergent can be reduced without decreasing the amount of combustion acid that can be neutralized, or the user may choose some combination of the above to fit his or her particular requirements. A variety of strong bases that can effectively be immobilized in the oil filter and that are effective neutralizing agents include barium oxide, calcium carbonate, calcium hydroxide, calcium oxide, magnesium carbonate, magnesium hydroxide, magnesium oxide, sodium aluminate, sodium carbonate, sodium hydroxide, zinc oxide, or mixtures thereof.
Like U.S. Pat. No. 5,164,101, PCT publications WO2006/066767 and WO2006/066768 each disclose aspects of a lubricant containing a minor amount of certain weak bases (oil-soluble succinimides) in combination with an immobilized base to remove combustion acids from circulating oil in an internal combustion engine, in particular those engines with exhaust gas recirculation systems (EGR) wherein the EGR does not have a chemical filter. The two publications disclose improved performance when particular molecular weight succinimides are employed in contrast to the earlier issued U.S. Pat. No. 5,164,101.
Other U.S. Patents and U.S. Patent Applications have disclosed the optimization of different aspects of a strong base oil filter. For example, U.S. Pat. No. 6,537,453 B2 discloses a specific design of an oil filter using one of three acid-neutralizing compounds; i.e. crushed limestone, calcium carbonate or magnesium carbonate.
U.S. Patent Application 2006/0000760 A1 teaches a specific oil filter design containing a venturi device to control oil pressure in order to direct oil flow to the acid-neutralizing compound in the oil filter.
U.S. Patent Application 2004/0178142 discloses an integrated paper having active particles immobilized therein wherein the paper comprises a plurality of fibrillated fibers having an average diameter of less than about 1000 nm and the pore size of the paper is less than or equal to about 2 μm. A list of active agents that may be immobilized includes magnesium oxide. The application further discloses lubricant oil filtration devices comprising the integrated paper in contact with lubricant oil.
U.S. Pat. No. 7,250,126 B2 discloses a process for incorporating a strong base into paper that is then used as a filter media. This application further highlights the value of choosing a strong base that has low molecular weight and divalent chemistry in order to minimize the grams of strong base required. Additionally, U.S. Pat. No. 7,250,126 B2 discloses acid-neutralizing filter media for a liquid filter in a liquid filtration system and further discloses that strong base particle diameters of greater than 10 microns are known to cause increased engine wear in engine lubrication systems. U.S. Pat. No. 7,250,126 B2 also discloses the use of adhesive binders to form strong base agglomerates in strong base filter elements.
U.S. Patent Publication 2006/0261004 A1 discloses that the capacity of a strong base oil filter is directly related to the surface area associated with pores of a defined minimum diameter.
U.S. Patent Publication 2006/0260874 A1 discloses that the use of a strong base filter to replace detergent in the lubricant may allow reductions or elimination of detergents in the oil that in turn may result in modulation of piston deposit levels, improved emission treatment equipment efficiency, or improved performance of the ubiquitous anti-wear oil additive, zinc dialkyldithiophosphate (ZnDDP).
However, these disclosures have not led to commercialization of an oil filter containing a strong base. Strong base migration from the filter to the lubricant remains an issue. Attempts to limit base migration (and related excess engine wear) have led to reduction in neutralization capacity of the strong base through, for example, reduction in reactive surface area. There remains a long felt need to achieve combustion acid neutralization without the need for high levels of ash-containing detergents in the lubricant and/or buildup of detergent-related piston deposits. It is an object of this invention to provide a commercially viable strong base-containing oil filter that may achieve combustion acid neutralization without the need for high levels of ash-containing detergents in the lubricant and/or buildup of detergent-related piston deposits.
New and better filter elements that, in use, can sequester acidic compounds in non-aqueous liquids and gaseous fluids are needed. In lubricating oils for internal combustion engines, sequestration may extend the life and usefulness of detergents in the fluid and extend intervals between oil drains. Further, other types of oxidation are inherent in systems where oxygen is present. These oxidations generate organic acids and the rates of these processes are acid-catalyzed. Once formed, these organic acids are not usually neutralized by dispersants or detergents and increased levels of these acids lead to even higher rates of their generation. Their rates of formation may be inhibited by reducing the levels of these acids through sequestering and/or neutralizing of acids in the strong base matrix, which may, in turn, extend the useful life of the fluid. If anti-wear agents in the fluid are degraded by acids, then passing fluids through a strong base filter element matrix may extend the useful life of the anti-wear agent. If anti-oxidants in a fluid are degraded by peroxides, then the sequestering of acids in a strong base matrix, which results in lowered oxidation rates, may extend the useful life of the fluid. The present invention is directed to these and other important ends.